1. Field of the Invention
The invention relates to axle/suspension systems for wheeled vehicles, and in particular to trailing arm rigid beam-type or spring beam-type axle/suspension systems for wheeled vehicles. More particularly, a first embodiment of the invention is directed to a trailing arm rigid beam-type axle/suspension system for trucks and tractor-trailers in which the axle is securely and efficiently mounted directly to the beams without any additional mounting hardware such as bolts, brackets and the like. A second embodiment of the invention is directed to a trailing arm spring beam-type axle/suspension system for trucks and tractor-trailers in which the axle is securely and efficiently mounted to the beams using minimal additional mounting hardware. A third embodiment of the invention is similar to the first embodiment, but uses bolts to assist in mounting the axle directly to the beams instead of welds, but still is free of additional hardware such as brackets and the like. All three embodiments of the present invention result in a lightweight, economical and sturdy axle/suspension system which limits fatigue stress on the axle/suspension system caused by various loads experienced by the vehicle during operation.
2. Background Art
The use of air-ride trailing arm rigid beam-type axle/suspension systems has become very popular in the heavy-duty truck and tractor-trailer industry. Air-ride trailing arm spring beam-type axle/suspension systems also are often used. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of longitudinally extending beams. Each beam is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending frame rails which depend from the trailer. More specifically, each beam is pivotally connected at one of its ends to a hanger which is attached to and depends from a respective one of the frame rails. An axle extends transversely between and typically is mounted on the beams anywhere from about the midpoint of each beam to the end of the beam opposite from its pivotal connection end. The opposite end of each beam also is connected to a bellows air spring or its equivalent which in turn is connected to a respective one of the trailer rails. A brake assembly and shock absorber typically also are mounted on each of the beams and/or axle. The beam may extend rearwardly or frontwardly relative to the front end of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term xe2x80x9ctrailing armxe2x80x9d will encompass beams which extend either rearwardly or frontwardly with respect to the front end of a vehicle.
The beam on which an axle is mounted typically either is a top mount or overslung beam or a bottom mount or underslung beam. An axle is mounted on the top of and is supported by the bottom mount or underslung beam-type, with generally the upper half of the axle being exposed. However, welding alone typically is inadequate to maintain the integrity of the axle to beam mount in underslung beams, since the predominant vertical axle loads placed on such beams are of the tensile rather than the compressive type. Inasmuch as welds tend to withstand compression better than tension, underslung axle to beam mounts must be fortified in some manner to maintain the mount integrity and prevent separation of the axle from the beams. Such fortification usually includes additional mounting hardware such as U-bolts, brackets and the like, resulting in a secure axle to beam mount more capable of withstanding tensile loads. However, such hardware adds unwanted cost and weight to an axle/suspension system. Examples of underslung axle/suspension systems which utilize significant additional axle to beam mounting hardware include U.S. Pat. No. 5,288,100 to Neway and 5,039,124 to Computer Design Chassis.
Conversely, an axle is mounted on the bottom of a top mount or overslung beam, with generally the lower half of the axle being exposed. The predominant vertical axle loads placed on top mount beams result in compression rather than tension. As noted immediately above, welds used to mount an axle to a beam withstand compression loads much better than tension loads. Thus, the majority of axle/suspension systems in commercial use today that are generally free of significant additional axle mounting hardware utilize top mount beams. Unfortunately, however, other forces such as torsional and fore-aft loads challenge the integrity of welds used as the sole means for mounting an axle to overslung beams, by causing tension in such welds. Therefore, many top mount axle/suspension systems also augment the axle to beam weld mounts with additional mounting hardware, but again sacrifice weight and cost efficiencies. Examples of overslung axle/suspension systems which utilize additional axle to beam mounting hardware can be seen in U.S. Pat. No. 4,693,486, 4,858,949 and 5,11 6,075, all of which are assigned to Lear Siegler, and U.S. Patent No. 5,328,159 assigned to Dana.
An example of a prior art axle/suspension system that has eliminated some of the additional hardware and utilizes only welds to secure the axle to a top mount beam can be found in U.S. Pat. No. 5,375,871 assigned to Ridewell. The upper portion of the axle is seated in a discrete shell member having a curved configuration which is complementary to the curvature of the axle, and elongated welds which extend generally adjacent to the lower ends of the shell are used to secure the axle to the shell. Although such an arrangement secures the axle to the beam, during operation of the vehicle the beam is subjected to various types of loads as discussed hereinabove, some of which can result in fatigue stress and cause cracking at the toes of the horizontal welds as well as in the axle itself. More specifically, torsional loads caused by trailer or suspension roll are transmitted through the bottom plate of the beam to the axle via the horizontal welds, thus creating stress concentration areas adjacent to the weld toes. Moreover, longitudinal or fore-aft loads created by movement of the axle/suspension system through a generally vertical arc during normal operation of the vehicle, which arc includes a longitudinal component, also adversely affect the aforementioned horizontal welds. Vertical and lateral loads also contribute to this problem. The relatively loose seating of the axle in the shell, whereby areas of clearance exist between the outer surface of the upper portion of the axle and the lower surface of the shell, intensifies the stress placed on the welds by the various loads. More particularly, especially during conditions of trailer lean which causes the aforementioned torsional loads, the horizontal welds are subjected to a cycling range of tensile and compressive loads, and areas of clearance between the axle and beam mount widen this cycling range thus placing increased stress on the welds. U.S. Pat. No. 2,660,450 assigned to Pointer-Willamette; 4,615,539 to Lear Siegler; 5,112,078 to Neway; and 5,634,655 to Watson and Chalin Manufacturing, all disclose arrangements similar to that shown in the ""871 patent to Ridewell.
Examples of bottom mount axle/suspension systems, which similarly attempt to mount the axle to the suspension beams using only welds, can be seen in the ""871 patent to Ridewell and the ""655 patent to Watson and Chalin discussed hereinabove.
A first embodiment of the present invention solves the problem of securing an axle to either top mount or bottom mount rigid suspension beams without the addition of any costly additional support parts and labor to assemble those parts, which also add unwanted weight to the suspension assembly. A second embodiment of the present invention provides a solution to mounting an axle on either top mount or bottom mount spring suspension beams using minimal additional mounting hardware. A third embodiment is similar to the first embodiment, but utilizes bolts to assist in securing the axle to the beams instead of welds.
These problems have been solved by the present invention through the use of a pre-assembled rigid or spring beam having an axle mounting plate formed with a recess which can range from significantly smaller than to generally the same size as the smallest axle which will be seated therein, and by seating the axle in the recess under force sufficient to deform a round axle into a generally oval or elliptical shape at the area of axle mounting to the beam. Such a tight fit eliminates, clearance and creates intimate contact between the axle and the axle mounting plate of the beam so that a preload or compression occurs at the interface between the outer surface of the axle and the axle contacting surface of the axle mounting plate. This intimate contact strengthens the axle against loads and resulting stresses encountered during operation of the vehicle and eliminates the need for an unusually robust beam and significant accessory hardware for supporting the axle. More specifically, this preload, which can also be described as a constant or continuous load exerted on the axle by the axle mounting plate, maintains the welds, or other fastening means such as bolts used to assist in securing the axle to the beam, in compression rather than tension. Other features of the present invention which contribute to solving problems encountered with prior art overslung and underslung trailing arm axle mounts such as described hereinabove, include the utilization of continuous welds disposed in windows formed in the axle mounting plate of the beam and which are circumferentially offset from the interface of the ends of the axle mounting plate and the axle. Alternatively, huck bolts, rivets or other fastening means can be used instead of welds in the same location. This strategic placement of the welds or bolts, in combination with the preload placed on the axle by the axle mounting plate, especially adjacent to the welds or bolts, effectively prevents stresses from damaging the fastening means of the axle by preventing loads from being transferred from the beams directly through the welds or bolts and into the axle. In the case of top mount rigid beams, another feature of the present invention is a decrease in the vertical distance from the top of the mounted axle to the top plate of the beam over that found in many prior art top mount rigid beams, in order to reduce clearance problems between the beam and the bottom of the trailer frame such as in low ride-height applications. The lack of material in the beam in the axle mount area caused by this decrease is compensated for with an insert contained within the beam adjacent to the axle mount area, and which is welded to the beam utilizing a single weld, consisting of one or more passes, which also welds beam sidewalls to the beam axle mounting plate.
Objectives of the present invention include providing a trailing arm axle/suspension system for wheeled vehicles, in which the axle is securely mounted to the suspension beams without the use of any additional parts or structure or alternatively using only minimal additional parts or structure.
Another objective of the present invention is to provide such a trailing arm axle/suspension system which can be assembled using as few as or fewer steps than assembly methods for prior art trailing arm systems.
A further objective of the present invention is to provide such a trailing arm axle/suspension system which is lighter and more cost effective than prior art trailing arm axle/suspension systems.
Still another objective of the present invention is to provide a trailing arm, top mount rigid beam-type axle/suspension system, which provides improved clearance between the beam and the vehicle frame in the axle mount area.
These objectives and advantages are obtained by a vehicle axle/suspension assembly, the general nature of which may be stated as including at least one suspension beam mounted on a frame of the vehicle, the suspension beam comprising an axle mounting plate formed with a recess, the recess having a shape generally complementary to and surrounding about half of the periphery of an axle, the axle mounting plate having a pair of edges defining the outermost limit of the recess, the recess being sized in the range of significantly smaller than to generally the same size as the surrounded axle periphery prior to mounting the axle on the axle mounting plate, and fastening means being circumferentially offset from the recess edges and a vertical axis plane of the axle, for securing the axle mounting plate to the axle.